As a sealing-end structure for a superconducting cable, the structure shown in FIG. 2 has been known, for example (see Patent literature 1). This sealing-end structure is provided with the following members:                (a) an end portion of a superconducting cable 100,        (b) a coolant vessel 101 for housing the end portion,        (c) a bushing 102 for providing electrical continuity between the superconducting conductor of the cable 100 and the normal-temperature side,        (d) a vacuum container 103 placed so as to cover the periphery of the coolant vessel 101, and        (e) a porcelain bushing 104 mounted on the vacuum container 103 so as to be erected at the normal-temperature side.        
The bushing 102 is placed from the inside of the coolant vessel 101 to the inside of the porcelain bushing 104 and is provided with the following members:                (a) a conductor portion 102a that is located at the center portion and that is electrically connected to the superconducting conductor through a joint 105, and        (b) a solid insulating layer 102b formed with fiber-reinforced plastic (FRP) around the conductor portion 102a so as to cover it.        
The bushing 102 is provided with two flanges 102c and 102d on its outer circumference. The flange 102c of the two is fixed to the coolant vessel 101, and the other flange 102d is fixed to the vacuum container 103 and the porcelain bushing 104. The coolant vessel 101 is filled with a liquid coolant, such as liquid nitrogen, for cooling the bushing 102, the joint 105, and the like. The porcelain bushing 104 is filled with an insulating fluid such as insulating oil or sulfur hexafluoride (SF6) gas. A metallic seal is applied between the flange 102c and the coolant vessel 101 and between the flange 102d and the porcelain bushing 104 to seal the coolant vessel 101 and other members airtightly. To reduce the heat intrusion from the normal-temperature side to the cryogenic-temperature side, the vacuum container 103 is provided with an intermediate vacuum portion 103a, which is a space enclosed by the flanges 102c and 102d and the members for connecting the flange 102c with the flange 102d.     Patent literature 1: the published Japanese patent application Tokukai 2002-238144.